In fiction, a common revelation is that the protagonist and antagonist were trained by the same mentor. This is occasionally taken even further by the revelation that another important character is the one who trained the mentor, and so on up the line.

When done well, this can add to the drama and development of the story and characters. It also allows for the comparing and contrasting of characters using similar skill sets at varying levels of mastery. When done badly, it can come off somewhere in the range of an Ass Pull or Contrived Coincidence. Either way, it's generally a concession to the Law of Conservation of Detail.

As noted above, an inevitable result of this chain, if it gets long enough, is one link having to fight another. Also, the problems of one of the prior masters may end up dropped in the lap of the latest disciple.

Chains should consist of at least three characters who can be connected in a straight line (in other words, character A trained character B who went on to train character C). The chain can branch out in more than one direction, but just one master training two apprentices doesn't count.

The primary one begins with Mutaito, who taught Masters Shen and Roshi, the Crane and Turtle Hermits. Master Roshi went on to train Son Gohan, Sr. and, between them, taught Son Goku. Finally, Goku found a disciple at the end of the series in Uub, the reincarnation of Majin Buu.

As for the Crane Hermit, he went on to train Tenshinhan and Chiaotzu.

One could also make an argument for Piccolo > Son Gohan > Videl.

Master Roshi's other student, the Ox-King, taught his daughter Chi-Chi, who trained her second son, Son Goten.

Also Goku(+ the teachings from his chain) and Piccolo (Namekian techniques) > Gohan > Goten, combined with Vegeta (Saiyan techniques) > Trunks gives Gotenks one of the most versatile move-set of the entire series, probably only passed by Cell who could use Frieza's techniques as well.

At some point before the "Son Goku and His Friends Return" special Gotenks also picks up Tien and Yamcha's moves, either by observation or training.

In the alternate future (meaning, the future that would have happened without any time traveling arcs), Piccolo > Son Gohan > Trunks.

The Hokuto Shinken style from Fist of the North Star is passed on through a singular line of successors that spans over 1,800 years and 64 grand masters. At the tail end of the chain is Kenshiro, who inherited the deadly martial art from Ryuken (Kasumi Ramon), who succeeded his older brother Kasumi Kenshiro, main character of Fist of the Blue Sky, who learned the art style from his father Kasumi Tesshin.

In Tenshi ni Narumon Mikael is a mentor to Noelle, just as Raphael was a mentor to him.

There is an example in the 2003 anime version of Fullmetal Alchemist. Ed and Al were trained by Izumi, who was trained by Dante. The symbol on Ed's coat, Al's armor, Izumi's collarbone, and Dante's wall seems to be a sort of crest, to indicate who studied under whom.

In the Saiyuki anime and manga series, this is how the Tenchi Kaigen sutras are passed from one sanzo priest to another (at least in East Asia, it may work differently in Tibet). Of the current crop of sanzos, Ukoku and Genjyo both inherited their sutras directly from the sanzos who trained them, Koumyou and Goudai, respectively. Koumyou and Goudai both studied under Abbot Jikaku (not a sanzo but still one of the most powerful Buddhist priests in China up until his death) as novices, making a 3-generation chain on either side of the current Minus Wave conflict.

From the prequels trilogy of Star Wars we learn that it goes: Yoda > Count Dooku > Qui-Gon Jinn > Obi-Wan Kenobi > Anakin Skywalker > Ahsoka Tano (Ahsoka is only in The Clone Wars animated series but she has been declared canon)

In the original trilogy Obi-Wan told Luke that Yoda was "the Jedi master who taught me" (which can be explained by it simply referring to Yoda training all the Younglings before they are Padawans) thus it becomes Yoda > Luke Skywalker > The new Jedi.

Ranger's Apprentice has a slightly unusual version. Halt trained Gilan. Gilan became a full Ranger, and Halt took on another apprentice, our protagonist Will. Gilan then at various points helped teach Will. Will himself has helped train a few apprentices, but briefly and he wasn't their master. Word of God says Will will not receive his own proper apprentice until the last book.

Myth Adventures gives us a chain consisting of Garkin and later Aahz > Skeeve > Massha

The Dresden Files is developing a chain with Ebenzar McCoy > Harry Dresden > Molly Carpenter. McCoy also taught Harry's mother, and Turn Coat reveals that McCoy is part of a long one stretching back all the way to the original Merlin.

Harry Potter received more than the standard Defence Against the Dark Arts training - Lupin, for example, gave him some exclusive tutelage. Harry then founded Dumbledore's Army and passed everything he knew to them. Later Neville, formerly a trainee of the D.A., continued Harry's legacy.

Done by entire species in the Uplift series. A species is formally designated by its chain of uplifters and by those species it has uplifted, and a species' prestige in galactic society is largely determined by the prestige of their chain.

The Matthew Swift series has Robert Bakker > Matthew Swift > Dana Mikeda; as of the end of the second book Matthew has acquired another apprentice, Penny Ngwenya.

In the Discworld novel Lords and Ladies, Granny Weatherwax lists a series of witches, her master, her master's master, etc. Subverted in that only one of those witches had even been mentioned in any other book.

There's also John Keel > Sam Vimes > Sam Vimes (via time loop) > Virtually everyone else in the watch. And since Vimes' training is highly valued across the Disc, we can assume there are a few watchmen being trained by his graduates.

Fitz of Robin Hobb's Farseer and Tawny Man trilogies is at the center of a few of these. Fitz was apprenticed, in different areas, to Verity, Burrich, and Chade; later, Fitz becomes master to Verity's son Dutiful, Burrich's son Swift, and...Chade himself.

In Steve Perry's Matador series, the chain of training in an unarmed martial combat form called "The 97 Steps" is Diamond > Pen > Khadaji > the Matadors. A Master/Apprentice reversal chain also figure into the works with Red teaching Khadaji to use spetsdods, then Khadaji teaching Red The 97 Steps. Additionally, one of the antagonists in the book, The Machiavelli Interface Massey, is revealed to have learned under Khadaji as well, by enrolling in the Matador's training school.

Since every clan cat in Warrior Cats has a mentor, there are often long chains of apprentice to mentor. This can get really convoluted when cats switch clans, seeing as the more recent ThunderClan medicine cats can trace their roots back to the early ShadowClan. Also, there are other funny coincidences.

Firestar, leader of ThunderClan was trained by the previous leader Bluestar, whose mentor was Sunstar, the leader before her.

Dustpelt trained both Squirrelflight and Ashfur. Ashfur hates Squirrelflight with his entire being.

In the Dragonsbane series knowing a mage's Master Apprentice Chain or 'line' tells you all kind of things about the type of spells they are likely to know and avoid.

The second Knights of the Old Republic notes Reven had such a chain it may or may not be a slip up that Kreia and Arren Kae, the handmaidens mother, are both identified as having been both his first and last.

In the Street Fighter series, Ryu and Ken were trained by Gouken, who himself was taught by Goutetsu. Ken would later go on to take Sean in as his student, while Ryu would indirectly mentor Sakura (who based her fighting style on his own).

In the Modern Warfare series, a clear line of progression can be seen between the various viewpoint characters, going in the order MacMillan > Price > Soap > Roach. Unfortunately, the chain is cut short by the deaths of Roach and Soap.

Homer to Virgil to Dante. Sort of, Virgil saw Homer as his greatest inspiration and Dante felt that Virgil had been his guide in the epic poetry but none of them ever met.

Don't forget John Milton, who read all three of these poets assiduously in their respective languages and set out to surpass them! And the age of great epics doesn't quite end with Milton...

Truth in Television in music: Teaching has always been considered part of the job of every eminent musician. For instance, virtually every professional pianist today is a seventh-, eighth- or ninth- generation pupil of Franz Liszt.